Method of coating and article produced thereby



Patented June 6, 1933 UNITED STATES PATENT OFFICE RALPH A. JACOBSON, F OMAHA, NEBRASKA, AND JOHN L. KEATS, OF WILMINGTON,

DELAWARE, ASSIGNORS TO E. I. DU PONT DE NEMOURS & COMPANY, OF WIL- MINGTON, DELAWARE, A CORPORATION 01 DELAWARE METHOD OF COATING AND ARTICLE PRODUCED THEBEBY No Drawing. Original application filed June 12, 1829, Serial No. 370,450. Divided and this application filed July 17, 1930. SerialNo. 468,727, and in Great Britain February 14, 1980.

- This invention relates to the art of coating compositions and, more particularly, to coating compositions and systems of coating compositions which are adapted to relatively 5 rapid drying schedules. 7

It has long been customary, in the finishing of articles with a series of coatings of paint, to allow one coating to thoroughly dry before a succeeding coating was applied. In

10 the automobile industry, however, where speed of production is a material factor in .keeping costs down, many efforts have been made to facilitate the painting operations. In one of these methods air drying is replaced by baking but, while this results in a It has therefore been customary in recent years to build up the complete coating systorn by applying a series of non-pyroxylin undercoatings to secure good adhesion to the metal of the body and form a good base, baking each of these coatings separately, and

then finishing by the application of one or more pyroxylintop coatings, accompanied by suitable sanding operations.

The present invention is directed generally to the system of coatings below-the top coatings, which series of coatings will be referred to herein as the undercoating system, and

primarily to the surfacer coatings.

The present invention is also directed primarily toundercoating compositionsQand undercoating systems which are free from 4:, cellulose derivatives, to the methods of making and applying such undercoating compositions and systems and to articles provided with such undercoating systems.

By the terms polyhydric alcohol-polybasic acid resin, as used herein, we mean products which comprise the reaction product of one or more polyhydric alcohols, at least one polybasic acid, with or without monobasic acids, and one or more oils or oil acids, and/or natural gums. 7

By the terms oil type or oil type vehicle, as used herein, we mean products which contain appreciable quantities of drying or semi-drylng oils and include natural gums or synthetic gums, such' as ester gum modified phenol formaldehyde resins and other phenol formaldehyde rosin condensation products; we also include polyhydric alcoholpolybasic acid resin varnishes formed by heating a preformed polyhydric alcohol-polybasic acid resin with the desired oil or oils according to regular varnish procedure.

By the term primer, as used herein, we mean coating compositions which, in addition to possessing any other properties specificallymentioned in connection with them, are also adapted to fulfill the functions of products known in the art as primers, which are compositions that are used to provide adhesion between the succeeding coating and the surface to which the whole coating system is applied, such primers possessing properties of toughness, flexibility, adhesion to the surface over which they are applied, and ability to resist penetration by the solvents of coatings applied thereto.

By the terms surfacer. and surfacer coating, as used herein, we mean coating compositions which, in addition to possessing any other properties specifically mentioned in connection with them, are also adapted to fulfill the functions of products known in the art as surfacers, whichare compositions that are used to fill up irregularities and permit sanding in order to obtain a smooth surface for the reception of the finishing coatings,

such surfacers posses ing the properties of high build, toughness, flexibility, adhesion to the coatings over which they are applied, and ability to resist penetration by the solvents of coatings applied thereto.

By the term polyhydric alcohol-polybasic acid resin surfacer, as used herein, we mean; a surfacer in which the major proportion of the film forming ingredients other than pigment is one or more polyhydric alcohol-polybasic acid resins, as defined herein. 4

By the term oil type surfacer, as ilsed herein, we mean a surfacer in which the ma-' j or proportion of the film forming ingredients other than pigment is an oil type prodnot, as defined herein.

By the term free from cellulose derivatives, as used herein, we mean that the material referred to does not contain cellulose derivatives.

By the expression ratio of pigment t0.- binder, as used herein, unless otherwise qual-' ified, we mean to include the total pigments -and fillers in the term pigment, and to include all the non-volatile constituents of the vehicle, such as oil, polyhydric alcohol-polybasic acid resin, natural resln, drier and softener-,in the term binder., the ratio being expressed on a weight basis.

By the term oil content, as used herein, we mean the number of gallons of oil per 100 pounds of gum, commonly called the oil length, when referrin to oil type vehicles, and the per cent of oil in the reaction product when referring to polyhydric alcohol-polybasic acid resins.

By the term units of oil, asused herein,

in' a second drying operation, provided the surfacer has the characteristics indicated below.

. We have also discovered that it is possible to apply all the coatings of .the undercoating system in rapid succession without intermediate baking and then dry all of these coat- .ings in a single operation provided certain precautions are taken, as set forth in detail hereinafter.

It is thereafter an object of this' invention to provide coating compositions which will set. up quickly ,when applied as thick films.

It is another object of this invention to provide a system of. undercoating in which .a plurality of coatings may be applied one after another without intermediate baking and bedried by a single drying operation.

It is a further obiect of this invention to provide a system of undercoatingin which all of. the undercoatings may be applied one after another without intermediate baking and be dried by, a single baking or air drying operation.

It is a still further object of this inventi n to provide a system of undercoating automo iles in which the entire system.may be applied and dried in not to exceed 3 hours at 160 F., or its equivalent period at a different temperature.

It is also an object of this invention to provide a method of control for the manufacture of coating compositions and undercoating systems which will permit rapid drying by a single air drying or baking operation mto a .film possessing all of the desired characteristics of flexibility, adhesion, sanding,

texture, toughness, hardness, heavy build,

ed several typical examples of undercoat- Polyhydnc alcohoFpolyoaeic acid resin aurfacera Example 1 Exam le 2 Oxide type Gray In ants: l ante:

ron oxide Imnpblack. Asbestlne China clay.. 361110 flxe arge Llthopone. 62 Carbon black. 11 Barytee 7. 25 Silica 8. 71 Non-volatile vehicle:

Polyhydric aleohol-polybasic acid resin 10 83 roliliifililbifi i bifiiidR555 C 10. 70 Ester gum 2. 13 Dibutyl phthalate 63 ion Eugen 054 Solvents:

Hi-flash naphtha 29.10 31. 506 Mineral spirits 12. 97 4.18

on b'ggtai "i flgnnBifiih. 100.00 100.00

a tion units of on com tionnig ..I .BEZ 34.01 1125 ll abeorpt on uni 100 22 2 mo 41 5 Ratio of of on Oil type aurfacers Example 3 Example 4 Oxide type Gray type 11. 88 ll. 87 79 10 16.79 15. 92 38. 75 39. so

2418]. China-wood-llnseed oil varnish. a a5 a 4i S ;:1 'i" d'l t' peel ngre en Stearine pitch .30 .41 Solvents:

Mineral spirits 14. 66 15. 44 Xylene 9. 26 7. 83

Total 100. 00 100. 00

Gil

ref

OiZ type aurfacere-Oontinued Oil type patties Example 3 Example 4 if Emllilple Oxide type Gray type Oxide 81 16 Gray Exallpple &3: Oxide stpmy Gray Oil absorption units 01 pigment combina- (same as s (saiiiia as knife ti 17.03 16.44 Example We Example 1 a sorp ion un s 1 Ratio 01 Units or on 1 1 Ingredients Pigments As examples of suitable primers and put- 5x33? 11-88 13-68 "156i ties for use with our new surfacers, especially g g black- -3; 3g I u 81' S in single baking systems, or in systems. In Whiting 38.75 44.66 39.80 45.69 which all the surfacers are baked simultanef {l ously, We have set forth the following: linseed oilvmishn M5 E69 r Drier 22 23 22 23 s i iii' iiii 30 z; 41 23 me p1 P Solvents:

Mineral spirits 14. 66 13. 35 15. 44 1s. 12 Xylene 9. 26 7. 83

Exam- Total... 100.00 100.00 100.00 100.00 1 absortptionb 17 17 0e 1e 44 1 44 en com ina on... .03 6. yi R tlia iii a co 0 D 0 b 0i] absorption unite 1 b Oil oxide fill/47. 4 103/47- 4 11/49. 1 1m/4 1 Sic 8pm type Units oi oi] resan OX1 e type The resins referred to above were formed by heatlng together the following ingredients 1n In i 111 the proportions (parts by weight) set forth 3 1 a, g 22 M9 below until the acid numbers were those 1narnp ac 1.59 3.03 Asbestine" 3.73 a. 41 dlcated China clay 4. 73 4. 46 Talc 3. 78 3 54 Litharg5 35 Ingredients Resm A Resin B Besm C Non-volatile vehicle:

Polyhydrlc alcohol-polybasic acid resin 13.. 11.82 24-%al. China wood-linseed oil varnish 12. 40 Glycerol 23.1 19. 3 16.72 D1 1' V 21 Linseed oil acids 30. 8 9- 6 Solvents: Phthalie anhydride 46. 1 37. 6 26.91 Hl -fl88l1 naphtha 20. 85 China wood 0i1 13. 5 Mineral spirits". 18. 26 30. 08 R 1 i8. 17 Turpentine... 6. 97 China wood oil acids 38- 20 Toluene 26. 62 28. 15

100.0 100.0 100.00 I T01; I 100.00 100.00 Acid number 30 20 01] absorplon #1111158! pigmgnt 00l11b1flfltl0ll. 36. 9 43. 77 Ratio of m S 100/65 7 100 84. 1

Units We have found it deslrable, however, 1n'mak-- Polyhydric aleohol-polybesic acid resin patties Exam- Examle 7 pie 8 xide Gray knife knife WP im Non-volntil icle Polyhydric aleohol-polybesic acid resin A. 12. 29 Poiyhydrie aicohol-polybesic acid resin C. 13. 30

Units of oil ing resin C, to heat the glycerol and phthalic anhydride until a homogeneous resin is obtained, then work in the rosin, and finally add the China Wood oil acids and heat to the desired acid number.

In the above examples the vehicle used in the oil type compositions may be made with any of the ordinary varnishg'ums in conjunction with China wood oil and linseed oil, provided there is a preponderance of China Wood oil.

In the above examples the quantities of drier indicated refer to amounts of a mixture of lead and manganese resinates'and linoleates, which mixture contains 14% lead and 4.5% manganese.

Examples ofsuitable systems embodying EXAMPLE 13 Oxide products The primer of Example 5 The putty of Example 7 The surfacer of Example 1 EXAMPLE 14 Oxide and gray products The primer of Example 5 The putty of Example 8 The surfacer of Example 2 OIL TYPE SYSTEMS 4 EXAMPLE. .15

Owz'de products The primer of Example 6 The putty of Example 9 The surfacer of Example 3 EXAMPLE 16 'Owide and grog products The primer of Example 6 The putty of Example 11 The surfacer of Example i MIXED SYSTEMS EXAMPLE 17 Orm'de products The primer of Example 5 a The putty of Example 10 The surfacer of Example 3 EXAMPLE 18- Om'de and gray products The-.primer of Example 6 The putty of Example 8 The surfacer of Example 2 As indicated by the above examples, the advantages of our invention may be obtained by either polyhydric alcohol-polybasic acid resin systems, oil type systems or combinations of these systems, and the putty and surfacer coatings may be of various types, such as oxide coatings or gray coatings. On account of the rapid drying of polyhydric valcohol-polybasic acid resin surfacers, howto have it specifically understood that the putty coating may be omitted from any of the systems indicated above, and from all of thesystems falling within the scope of our invention, provided the surface, to which the system of undercoatings is to beapplied,

' .is sufficiently smooth so that the putty coating is not needed to fill up irregularities in that surface, or if the standards of acceptable quality of the finished product do not demand the optimum results. We also desire to have it understood that the putty may be made of a consistency suitable forapplication' as a knife glaze, as indicated bythe in the systems of Exam les 13, 14, and 17 above, or may be diluted y volatile solvents,-

such as those disclosed herein, to enable it to be applied as a spray glaze. In practice however, we have found it convenient and satisfactory to also use the undiluted surfacers as spray glazes as indicated by the compositions of Examples 9 and 11 used in the systems of Examples 15 and 16 above.

While the specific characteristics necessary in an undercoating system vary with the particular product being painted, and the arbitrary standards of acceptability which are set up, it may be said in general that the characteristics of such systems, especially for automobile bodies, are substantially as follows:

Flewibilz'ty and adhesion.-The various coatings should adhere to each other and the complete built-up system should adhere to the metal and not chip off in relatively large pieces, but should tend to strip off as a ribbon when scratched. In other words it should show definite tendency toward chewiness when cut with a knife, and be of a non-shattering character, and it must not develop cracking and checking on normal weather- 1n iou/glmessr-When a knife is drawn across the surface with a scraping action the film should notchip or show chalkiness.

H ardmss.The film must offer considerable resistance to enetration or scraping off in the customary nger-nail test, in order to withstand sanding, and be hard throughout.

Sanding-In wet sanding operations the composition must not gum up the sandpaper, itmust not sand too hard or too slowly, and it must not have objectionable drag, that IS, an undue tendency to pull the paper out of the operators hand. I

Texture-The film must be sufiiciently free from grit so that objectionable scratching is not encountered during the sanding operations, and to avoid pull-outs, that is, dislodgment of gritty particles with the resulting blemishes in the surface.

M of porosity.-'The film must be sufliciently non-porous so that it will not exhibit an objectionable blotter action when the top coatings are applied, with a resultant sinking in of the latter. In practice nonporosity of the undercoatings is spoken of in terms of their holding out properties forv the color coating.

Pittz'ng.-The film must not show pitting, that is, very small depressions 1n the color coating which give the appearapce of pinholes.

Lz'fting.The film must not become loosened and shrivel, surface crinkle or induce pitting when the top coatings are ap- -plied compositions of Examples 7, 8, and 10 used or blisters on application of the top coating,

Popping-The film must not form bubbles due to the evolution of gas from the undercoating structure at localspots.

Feathering.The film must factorily, that is, when the operator cuts through the separate coatings there must not best jagged appearance between the exposed ed es of adjacent coatings.'

0ftem'ng.The film must not become soft or mushy under the action of water during the rubbing operations, and should not be rapidly softened under the action of petroleum thinners.

BuiZd'.-The film must dry satisfactorily in heavy coatings, such as are necessary to fill scratches and other irregularities in the surface to which the film is applied, and must give a smooth surface on sanding.

Drying.-The film must dry all the way through instead of being mushy at the bottom and hard at the top, which is known as case hardening, and it must dry with sufficient rapidity and uniformity so that it will not undergo further drying with contraction in volume, as these will lead to failures, such as checking and cracking, on normal exposure.

NOn-bZeeding.-Ingredients of the undercoatings must not be absorbed by the color coating so as to affect the shade or other qualities of the latter.

By our invention we are able to obtain all of the above characteristics, accompanied by the special ability to effect satisfactory drying of complete undercoating systems by a single short baking period, that is, by a single baking period of not over 3 hours at 160 F.

or its equivalent period at a different temperature. The five typical systems given in Examples 13-17 above will all meet these requirements and,when applied with one primer coating, one putty coating and one, twoor three surfacer coatings, have produced satisfactory films by baking 2 hours at 160 F. The typical system given in Example 18 is not adapted for drying by a single baking operation, but is especially adapted for a double baking operatiom in which theprimer is baked for 1 to 2 hours at 160 F. and then the putty and two or three surfacer coatin s are baked for an additional 2 hours at 160 In practice, where all the undercoatings are to be dried simultaneously, we have found it desirable to allow the primer coating to stand for a period of from five to fifteen minutes to allow the solvents to flash off, after which the putty is, applied as a knife glaze or spray glaze if a putty coating is to be used, and this is immediately followed by the application of the desired number of surfacer coatings, preferably by sprayingg without waiting for intermediate drying, i. e. for longer than ten minutes to allow partial evaporation of solvents, between these coatings. I The system is then dried by baking for feather satisnot to exceed 3 hours at 160 F., or its equivalent period at a different temperature.

Where a multiple baking is not objectionable the same procedure is preferably followed, except that the primer is preferably prebaked, e. g. for 2 hours at 160 F., and the putty and surfacer coatings are then applied and baked in a second operation for not to exceed 3 hours at 160 F., or its equivalent period at a different temperature.

In practice it has been found that the presence of a. large amount of solvent facilitates the leveling when a coating of surfacer is being sprayed, and it is therefore customary to dilute the coating composition with varying amounts of solvent according to the spraying viscosity desired. For example, the surfacers given in Examples 3 and 4 have been found to spray more satisfactorily when diluted with 10% by volume of mineral spirits.

The specific surfacer compositions which may be used in the carrying out of our invention may be varied within relatively wide limits, as follows:

The pigment combinations for both polyhydric alcohol-polybasic acid resinand oil type products may vary in regard to their chemical compositions and their physical properties:

((1) Their chemical compositions may vary Widely in iron oxide content for oxide products. In gray products the lithopone may be replaced by titanox or white lead pigments, and these may likewise be varied over wide limits. The lampblack may be replaced by other blacks, such as carbon black and Keystone filler. Fillers, such as asbestos, China clay, blanc fixe, barytes, silica, whiting, and talc, are generally interchangeable except for limitations as specified below. Likewise, when desired, a buff material can'be prepared by using lithopone and a yellow pigment, such as an ochre, in place of the iron oxide. In

the case of certain polyhydric alc0hol-poly-- also in the case of certain oil type vehicles' which tend to be reactive with basic pi ments, such as Congo-China wood oil varnis es, in-

'HIgS should be avoided as otherwise good anchorage or adhesion of'the top coatings to the undercoating system is likely to be sacrificed: Further, we have observed that a predominance of hard fillers, such as barytes and silica, should usually be avoided in putties and surfacers,'except in the case of products designed for bricking, due to the hard sanding properties they impart to surfacers. It is likewise desirable to select pigments and fillers of relatively good texture or fineness, as otherwise excessive and costly grinding is required to eliminate the grit which would cause objectionable sand scratching of the surface during sanding. Pigments. which lead tobleeding upon application of the top coatings should also be avoided. The oil absorption value of the pigment composition is of primary importance and is discussed indetail in the following paragraphs.

By the term oil absorption, as used herein, we mean the number of parts, by weight, of acid refined linseed oil, having an acid number of 6 to 8, which are required to wet 100 parts by weight of the pigment to a predetermined consistency. The total oil -absorption units for any given pigment combination is determined directly or by multiplying the weight of each pigment used, expressed in terms of percentage of the total pigment combination, by its oil absorption, and adding these figures.

For example, applyi this to the pigment combination of the sur acer of Example 2, the total oil absorption of the pigment combination is arrived at as follows:

While various methods may be used for determining the oil absorption of the pigments used, the values will vary with the method selected, and the figures given herein are based on the following spatula method, which was described in The Paint, Oil & Chemical Review for May 7, 1924, on page 10 and is the one we prefer to use:

Weigh out 5 grams of the pigment and spread it over a finely ground glass plate in a layer about 1 wide and 3 to 4" long. Substantially fill a 10 cc Lunge type pipette with the linseed. oil and weigh it. Add 20 drops of oil to one end of the pigment layer and mix these with a fairly stifi' spatula until a stiff putty-like paste is formed. Add. 5 drops of oil and work this into the paste 65 with a gentle but firm pressure until a seepy or other common grinding equipment.

paste is formed. Gradually add the untouched dry pigment until the paste becomes stitf again. Repeat until all the dry pigment is worked into a stiff putt -like ball, gradually reducing theamount 0 oil used. Add one more drop of oil and work this into the paste. Collect all the paste into aball and place it on the blade of a spatula, near the handle. Gently transfer the baltto a spatula having a blade by running the latter underneath the ball. Turn the spatula down and very gently throw the ball off. If no paste clings to the spatula add one more drop of oil and work it into the ball. Repeat until some paste clings to the spatula. pipette and calculate the oil absorption as grams of oil per 100 grams of pigment. All operations are carried out at 50% relative humidity at 25 C. in a constant temperature, constant humidity room.

Grinding.We have also found that the method and degree of grinding of the undercoatingl compositions has a material effect upon t e apparent oil absorption, that is, the original total oil absorption of the pigment combination may be either slightly or greatly increased according to the method and degree of grinding selected, the oil absorption increasing with the fineness of the grinding. The limits of. allowable determined oil absorption values of pigment compositions suitable for use as disclosed herein hold true irrespective of grinding conditions, but the ratio of oil absorption units to units of oil in the optimum products decreases with increased grinding. Our experiments have been based for the most part on short ball mill grinding procedures, which we have found to answer satisfactorily the grinding requirements. From.a practical viewpoint, however, the grinding may be done in a ball mill, buhrstone mill, roller mill, colloid nill,

uitable periods of grinding of the undercoating compositions for most pigment combinations are, for example, in the case of the ball mill, 6 hours with a charge of two parts by weight of balls to one part by weight of material; a single passage'through 30 or larger buhrstone mills; or aroller mill set to produce a corresponding degree of fineness.

The polyhydric alcohol-polybasic acid resins used in the polyhydric alcohol-polybasic acid resin compositions set forth above may be replaced by other polyhydric alcoholpolybasic acid resins which also have suflicient oil chemically combined therewith to give satisfactory solubility and flexibility Without materially retarding drying. For example, We have found that the oil content may vary from 23 to 50% in the case of linseed oil, and from 25 to in the case of China wood oil, based on the'weight of the dry resin composition. We may also use polyhydric alcohol-polybasic acid resins Reweigh the modified by natural gums chemically combined therewith to give satisfactory solubility, or polyhydric alcohol-polybasic acid resins modified by both gums and oils.

The non-volatile vehicles used in the oil type products may include any of the common natural gums, synthetic gums, such as ester gums, or Amberol or polyhydric alcohol-polybasic acid resins, as the gumconstituents of these vehicles. Suitable oils include China wood oil, linseed oil, perilla oil, soya bean oil, and fish oil, although we prefer to employ a mixture of China wood oil and linseed oil, with the former predominating over the latter. The presence of China wood oil seems desirable as such oil compositions appear to dry by polymerization at the expense of oxidation, and the polymerization enhances the rapid drying of the resultant films. Where linseed oil predominates over China Wood oil it appears preferable to select a vehicle of somewhat shorter oil length than in the case of the reverse type of vehicle. Perilla oil appears to behave much the same as linseed oil. Theuse of soya bean oil and fish oil generally leads to less satisfactory results, although the quality of the resultant products does not exclude them from the scope of this invention. Any desired mixtures of the oils indicated above, depending upon the rate of drying and other characteristics desired, may be used. The oil length" of the non-volatile vehicle should not be less than 8 gallons, and is preferably not less than 12 gallons.

The volatile solvents may likewise be varied in all of the above systems, but it Will be obvious'that solvents whose evaporation rates are so slow as to seriously impede drying at moderate baking temperatures'should not be used in sufiicient quantities to be objectionable. We have found that Hi-flash naphtha,

high boiling esters, turpentine, mineral spirits and toluene are desirable ingredients in polyhydric alcohol-polybasic acid resin products, although the Hi-flash naphtha and high boiling esters are not needed in oil type products. In the latter, mineral spirits, turpentine, xylene and toluene may beused separately or in various combinations with satisfactory results, although turpentine is especially useful when the product contains hard, natural gums. Similarly, in the polyhydric alcohol-polybasic acid resin products, the mineral spirits and toluene maybe omitted and replaced by Hi-fiash naphtha, high boiling esters or turpentine, although we have found, in general, that mixed solvents give better results in both polyhydric alcoholpolybasic acid resin and oil type products.

Although lead and manganese driers are indicated as having been used in the products sets forth above, it should be understood'that other well known suitable driers, such as cobalt driers, may be substituted therefor and that slight variations may be made in the amounts of drier used without materially altering the drying schedule. In the case of oil type products, however, the optimum rate of drying for the, composition under consideration can only be obtained by including sufficient drier in the composition.'

here desired, compositions falling within the scope of this invention may contain protective agents of various types, such as eugenol, to prevent objectionable skinning, stearine pitch to overcome objectionable pigment settling, and litharge to improve water resistance in certain polyhydric alcohoLpolybasic acid resin products. Likewise, softeners, such as dibutyl phthalate, may be used in polyhydric alcohol-polybasic acid resin products. I

In all of the systems falling within our invention we desire to have it understood that the top or color coatings applied may be of any desired type, whether pyroxylin, oil, or resin.

We have found -that drying at the lower temperatures, such as 160 F., is preferable, but that where 200 F. or 250 F. are not objectionable a 1 -hour drying at 200 F. or a 1-hour drying at 250 F. is equivalent to a 3-hour drying at 160 F. For convenience of reference we have stated our drying time in terms of drying at 160 F. We have also found that our undercoating systems will attain a satisfactory hardness in air drying, that is, at room temperature of about 7080 F., within approximately 1524 hours for polyhydric alcohol-polybasic .acidresin key to successful single bake undercoating flexibility and toughness of the resulting filmand to the lifting characteristics of the individual or collective coatings, as explained herein. 4 l

Our system of control, for'the carrying out of the above'discovery, and particularly for the production of coating compositions for usein systems in which all the surfacer coatings are dried simultaneously or in which the entire undercoating system is dried in one operation, is as follows: 4 I p Polyhydm'c alcohol-polybasio acid resin surfacers'.-Formulate these from pigment combinations whose total oil absorption units do ment to binder high enough to avoid lifting when the top coatings are applied and low enough to avoid undue brittleness and lack of toughness. This ratio, expressed in terms of oil absorption units to units of oil, should be between 100:20 and 100:60.

Oil type surfacera-Formulate these from pigment combinations whosetotal oil absorption units do not exceed 22, use a binder having an oil content of not less than 8 gallons, and maintain a ratio of pigment to binder high enough to avoid lifting when the top coatings are applied and low enough to avoid undue brittleness and lack of toughness. This ratio, expressed in terms of oil absorption units to units of oil, should be between 100:40 and 100:70.

While we have stated that pigment combinations whose oil absorption units do not exceed 50 and 22 are satisfactory for polyhydric alcohol-polybasic acid resin and oil type surfacers, respectively, we desire to have it understood that, as indicated by the compositions set forth in Examples 13-17, we prefer to use pigment combinations whose oil absorption units are appreciably less than 50 and 22 for polyhydric alcohol-polybasic acid resin and oil type surfacers, respectively.

It will be obvious that where the standards of acceptable quality are lower than those indicated above, or where longer drying periods or multiple bakings are not objectionable, greater variations in this method of control are permissible.

Primers.Although we have stated limits for the allowable maximum oil absorption value of the pigment combinations of surfacer compositions coming within the scope of this invention, our experience indicates that satisfactory primer compositions may be formulated by selecting pigment combinations having oil absorption values anywhere within the range of practical primer pigment compositions and formulating the primer compositions therefrom in the same general manner as the surfacers.

' This is particularly true when the primer is to be baked separately from the surfacer coatings, and when the entire undercoating system, including a relatively good surfacer, is to be baked in a single operation. However, if an oil type surfacer is used which is close to the limiting ratios of oil absorption units to units of oil, that is close to 100 :40 .or close to 100 :70, the primer must be formulated with greater care to' enable it to be dried simultaneously with the surfacer coat ings, and in such cases the primer should approach the composition of Example 6 above for the best results.

In so far as film quality is concerned, the optimum results are obtained with primer compositions having as low a ratio of oil absorption units to units of oil as is possible without encountering lifting of the dried complete undercoating system upon application of pyroxylin top coatin It is a particular feature o polyhydric alcohol-polybasic acid resin primers that they set up to a suflicient hardness to allow the application of a knife glaze as soon as the solvents flash off, which is ordinarily within 5 to 15 minutes. On the other hand, if an oil type primer, such as indicated in Example 6, is used it should be subjected to several hours air drying or to a short baking period, as for example 1 hour at 160 F., before a knife glaze is applied thereover.

Pwttz'ea-Both polyhydric alcohol-polybasic acid resin putties and oil type putties are formulated in the samegeneral manner as the surfacers except that they usually contain less solvent, but they may vary as discussed above.

By the term film thickness, as used herein, we mean the thickness of the complete undercoating system, or the complete series of surfacer coatings, after the dryingoperation and before sanding, which results from the application of the required number of coatings without lapping, that is without traversing the same area more than once for any given coating.

It is a particular feature of our invention that, by following the method of control set forth herein, in the light of the entire disclosure of this application, we are enabled to secure satisfactory undercoating systems by the simultaneous baking of a plurality of coatings whose combined film thickness is at least .003, thus making it possible to secure heavy build in conjunction with rapid drying schedules.

We desire to have it understood, however, that our invention includes the manufacture of the individual coatings when the system of control set forth above is utilized,,or when compositions of the range indicated herein are used in undercoating systems, and that it also includes the simultaneous drying of a plurality of-non-pyroxylin coatings which form a relatively'thick film regardless of whether these constitute the entire undercoating system.

It will therefore be apparent that we have developed new and useful coating compositions and undercoating systems which form films that possess all of the desired characteristics, that our coating compositions and systems can be dried in much less time than former compositions and systems, and that any or all of the desired undercoatings may be applied one after another withoutintermediate baking and dried at one time to a satisfactory hardness.

' No specific claims are made herein to coating compositions of the type set forth herein since these are claimed in our copending applications Serial Numbers 370,450 and 370,- 451, filed June 12, 1929. The present application is a division of Serial No. 370,450, and also embodies the subject matter of application Serial No. 468,728, which was a division of application Serial No. 370,451.

Similarly, no specific claims are made herein to mixed undercoating systems containing a separately dried oil type primer and a polyhydric alcohol-polybasic acid resin surfacer, as these features are claimed in our co-pending application Serial No. 370,452, filed June 12, 1929.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that we do not limit ourselves to the specific embodiments thereof except as defined in the appended patent claims.

We claim: I

1. The method of coating articles which comprises applying a primer, applying a plurality of surfacer coatings which are free from cellulose derivatives without any intermediate baking of the individual coatings but allowing at least a portion of the volatile solvents of one coating to evaporate before the application of the next coating, drying all of the surfacer coatings with a single drying operation to a state that will permit sanding, and applying a top coating thereover.

2. The method of claim 1, in which the drying operation comprises a single baking "for not to exceed 3 hours at 160 F., or its equivalent period at a different temperature.

3. The method of claim 1, in which the combined film thickness of the surfacer coatings is at least .003" and in which the drying operation comprises a single baking for not to exceed 3 hours at 160 F., or its equivalent period at a difl'erent temperature.

4. The method of claim 1. in which the surface'r coatings are polyhydric alcohol-polybasic acid resin coatings.

5. The method of claim 1, in which the surfacer coatings are oil type coatings.

6. The method of claim 1, in which all of the primer and surfacer coatings are oil type coatings.

7. The method of coating articles which comprises spraying them with a plurality of dissimilar coatings which are free from cellulose derivatives in rapid succession but allowing at least a portion of the volatile solvents of one coating to evaporate before the spraying of the next coating, drying said coatings simultaneously to a state that will permit sanding and applying a top coating thereover.

8. The method of claim 7, in which the second coating is different from the first coating.

9. The method of claim 7, in which the sec ond coating is diflerent from the first coating and in which at least two coatings are alike.

'10. The method of coating vehicles which comprises spraying them with a primer which is free from cellulose derivatives and subsequently with a plurality of coatings of surfacer which is free from cellulose derivatives Without any intermediate baking of the in: dividual coatings but allowingat least a portion of the volatile solvents of one coating to evaporate before the application of the next coating, then drying the entire system with a single baking for not to exceed 3 hours at 160 F.,- or its equivalent period at a different temperature,.to a state that will permit sanding, and applying a top coating thereover.

11. The method of coating vehicles which comprises spraying them with a primer, applying a putty, and then spraying them with a plurality of coatings of surfacer without any intermediate baking of the individual coatings but allowing at least a portion of the volatile solvents of one coating to evaporate before the application of the next coating, all of said coatings being coatings which are free from cellulose derivatives, drying the entire system with a single baking for not to exceed 3 hours at 160 F., or its equivalent period at a difi'erent temperature, to a state that will permit sanding, and applying a top coating thereover.

12. A metal article coated by the process of claim 1, in which the combined film thickness of the undercoating system after drying and before sanding is at least .003".

13. A metal article coated by the process of claim 10, in which the combined film thickness of the undercoating system after drying and before sanding is at least .003.v

14. A metal article coated by the process of claim 1, in which the combined film thickness of the undercoating system after drying and before sanding is at least .003", and in which the surfacer coatings comprise polyhydric alcohol-polybasic acid resin products.

of claim 10, in which the combined film thickness of the undercoating system after drying and before sanding is at least .003", and in which the surfacer coatingscomprise polyhydric alcohol-polybasic acid resin products.

16. A metal article coated by the process of claim 7, in which the combined film thickness of the coatings dried simultaneously is at least .003".

17. A metal article coated by the process of claim 7, in which the combined film thickness of the coatings dried simultaneously is at least .003", and in which the surfacer coatings comprise p'olyhydric alcohol-polybasic acid resin products.

18. The method of rapidly coating articles which comprises applying a primer, applying a plurality of oil type surfacer coatlngs with- 1 out any intermediate drying of the in ividual 15. A metal article coated by the process coatings but allowing at least a portion of the volatile solvents of one coating to evaporate before the application of the next coating, drying all of the surfacer coatings with a single drying operation to a state that will permit sanding, and applying a top coating thereover.

19. The method of claim 18, in which the drying operation. comprises a single baking for not to exceed 3 hours at 160 F., or its equivalent period at a different temperature.

.20. The method of claim 18, in which the combined film thickness of the surfacer coatings is at least .003" and in which the drying operation comprises a single baking for not to exceed 3 hours at 160 F.', or its equivalent period at a different temperature.

21. The method of coating vehicles which comprises spraying them with a primer which is free from cellulose derivatives and subsequently with a plurality of coatings of oil type surfacer which is free from cellulose derivatives without any intermediate baking of the individual coatings but allowing at least a portion of the volatile solvents of one coating to evaporate beforethe application of the next coating, then drying the entire system with a single baking for not to exceed 3 hours at 160 F., or its equivalent period from cellulose derivatives without any intermediate baking of the individual coatings but allowing at least a portion of the volatile solvents of one coating to evaporate before the application of the next coating, then drying the entiresystem with a single baking for not toexceed 3 hours at 160 F., or its equivalent period at a different temperature, to a state that will permit sanding, and applying a top coating thereover.

24. The method of claim 23, in which'all of the coatings are oil type coatings.

25. A metal article coated by the process of claim 18, in which the combined film thickness of the undercoating system after drying and before sanding is at least .003".

26. A metal article coated by the process of claim 21, in which the combined film thickness of the undercoating system after drying and before sanding is at least .003

27. A metal article coated by theprocess of claim 18, in which'the combined film thicktures.

RALPH A. JACOBSON.

JOHN L. KEATS. 4 

